I'm using split panes in tmux - one being vim, other shell. Sometimes, around once a day, vim freezes. I can move between panes, perform any tmux commands, just vim doesn't react to anything. This happens only with tmux. My only solution for now is to kill that pane and create new one.

This has never happened to me, and I have used tmux+Vim in that way extensively. This does not mean it cannot happen to you — but it means you will have to try to more precisely locate when it happens to try to figure out why. Relevant information is what terminal you are using. One idea: you are not just accidentally hitting Ctrl+S in the Vim window? In that case: press Ctrl+Q to "unfreeze".
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Daniel AnderssonFeb 17 '13 at 12:07

You can post it as answer and you'll get some reputation :)
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Ondrej SlintákFeb 17 '13 at 12:25

When you're just starting to use vim/terminal editors as your main editor, this is a very common problem. Later on, you'll end up having :wq spread throughout all your documents (or ZZ, I don't judge) and feel silly.
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RobJul 29 '13 at 15:14

Amazing how you correctly guessed the problem from such such a vague description. Thanks!
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NewWorldMay 30 '14 at 8:00

1

Holy ...! I've been having this issue for years, and never actually searched for a solution. This answer was the first solution I found, and it literally took me 3 seconds... All those hours wasted, and you had the solution just a couple of seconds away. I wish I could upvote you more (and downvote myself). Thanks!
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simendsjoOct 10 '14 at 21:29

Another time you might have this issue is when you're switching between editors (emacs and vim, for instance). They have different "save" commands, muscle memory confuses and hence the freezing.
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Utkarsh SinhaNov 11 '14 at 14:26

This being the accepted answer shows that the problem has nothing to do with tmux, but rather terminal flow control. Another way vim may appear frozen but tmux fine is to accidentally type a very processing-heavy command in normal mode. Ctrl-C does the trick, interrupting the command.
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Brian DuncanMar 4 at 4:34